共查询到20条相似文献,搜索用时 125 毫秒
1.
Aricó F Chang T Cantrill SJ Khan SI Stoddart JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(16):4655-4666
The template-directed construction of crown-ether-like macrocycles around secondary dialkylammonium ions (R2NH2+) has been utilized for the expedient (one-pot) and high-yielding synthesis of a diverse range of mechanically interlocked molecules. The clipping together of appropriately designed dialdehyde and diamine compounds around R2NH2+-containing dumbbell-shaped components proceeds through the formation, under thermodynamic control, of imine bonds. The reversible nature of this particular reaction confers the benefits of "error-checking" and "proof-reading", which one usually associates with supramolecular chemistry and strict self-assembly processes, upon these wholly molecular systems. Furthermore, these dynamic covalent syntheses exploit the efficient templating effects that the R2NH2+ ions exert on the macrocyclization of the matched dialdehyde and diamine fragments, resulting not only in rapid rates of reaction, but also affording near-quantitative conversion of starting materials into the desired interlocked products. Once assembled, these "dynamic" interlocked compounds can be "fixed" upon reduction of the reversible imine bonds (by using BH3.THF) to give kinetically stable species, a procedure that can be performed in the same reaction vessel as the inital thermodynamically controlled assembly. Isolation and purification of the mechanically interlocked products formed by using this protocol is relatively facile, as no column chromatography is required. Herein, we present the synthesis and characterization of 1) a [2]rotaxane, 2) a [3]rotaxane, 3) a branched [4]rotaxane, 4) a bis [2]rotaxane, and 5) a novel cyclic [4]rotaxane, demonstrating, in incrementally more complex systems, the efficacy of this one-pot strategy for the construction of interlocked molecules. 相似文献
2.
Tseng HR Vignon SA Celestre PC Perkins J Jeppesen JO Di Fabio A Ballardini R Gandolfi MT Venturi M Balzani V Stoddart JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(1):155-172
With the fabrication of molecular electronic devices (MEDs) and the construction of nanoelectromechanical systems (NEMSs) as incentives, two constitutionally isomeric, redox-controllable [2]rotaxanes have been synthesized and characterized in solution. Therein, they both behave as near-perfect molecular switches, that is, to all intents and purposes, these two rotaxanes can be switched precisely by applying appropriate redox stimuli between two distinct chemomechanical states. Their dumbbell-shaped components are composed of polyether chains interrupted along their lengths by i) two pi-electron rich recognition sites-a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) moiety-with ii) a rigid terphenylene spacer placed between the two recognition sites, and then terminated by iii) a hydrophobic tetraarylmethane stopper at one end and a hydrophilic dendritic stopper at the other end of the dumbbells, thus conferring amphiphilicity upon these molecules. A template-directed protocol produces a means to introduce the tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT(4+)), which contains two pi-electron accepting bipyridinium units, mechanically interlocked around the dumbbell-shaped components. Both the TTF unit and the DNP moiety are potential stations for CBPQT(4+), since they can establish charge-transfer and hydrogen bonding interactions with the bipyridinium units of the cyclophane, thereby introducing bistability into the [2]rotaxanes. In both constitutional isomers, (1)H NMR and absorption spectroscopies, together with electrochemical investigations, reveal that the CBPQT(4+) ring is predominantly located on the TTF unit, leading to the existence of a single translational isomer (co-conformation) in both cases. In addition, a model [2]rotaxane, incorporating hydrophobic tetraarylmethane stoppers at both ends of its dumbbell-shaped component, has also been synthesized as a point of reference. Molecular synthetic approaches were used to construct convergently the dumbbell-shaped compounds by assembling progressively smaller building blocks in the shape of the rigid spacer, the TTF unit and the DNP moiety, and the hydrophobic and hydrophilic stoppers. The two amphiphilic bistable [2]rotaxanes are constitutional isomers in the sense that, in one constitution, the TTF unit is adjacent to the hydrophobic stopper, whereas in the other, it is next to the hydrophilic stopper. All three bistable [2]rotaxanes have been isolated as green solids. Electrospray and fast atom bombardment mass spectra support the gross structural assignments given to all three of these mechanically interlocked compounds. Their photophysical and electrochemical properties have been investigated in acetonitrile. The results obtained from these investigations confirm that, in all three [2]rotaxanes, i) the CBPQT(4+) cyclophane encircles the TTF unit, ii) the CBPQT(4+) cyclophane shuttles between the TTF and DNP stations upon electrochemical or chemical oxidation/reduction of the TTF unit, and iii) folded conformations are present in which the CBPQT(4+) cyclophane, while encircling the TTF unit, interacts through its pi-accepting bipyridinium exteriors with other pi-donating components of the dumbbells, especially those located within the stoppers. 相似文献
3.
As the complexity of mechanically interlocked molecular architectures increases, it is important to understand the underlying principles, such as molecular recognition and self‐assembly processes, that govern the practice of template‐directed synthesis necessary to create these particular compounds. In this review, we explain the importance of dynamic processes in the synthesis of mechanically interlocked compounds. We show how many different dynamic covalent bonds have been used in the synthesis of rotaxanes, catenanes, and other higher‐order mechanically interlocked compounds, with the goal of revealing the state of the art in dynamic covalent chemistry. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 136–154; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20173 相似文献
4.
Operating molecular elevators 总被引:1,自引:0,他引:1
Badjic JD Ronconi CM Stoddart JF Balzani V Silvi S Credi A 《Journal of the American Chemical Society》2006,128(5):1489-1499
Inspired by the concept of multivalency in living systems, two mechanically interlocked molecules have been conceived that incorporate not once or twice but thrice the features of a pH-switchable [2]rotaxane with two orthogonal recognition sites for dibenzo[24]crown-8 (DB24C8), and 2,3-dinaphtho[24]crown-8 (DN24C8)-one a dialkylammonium ion (CH(2)NH(2)(+)CH(2)) and the other a bipyridinium dication (BIPY(2+)). Whereas at low pH, the CH(2)NH(2)(+)CH(2) sites bind the DB24C8/DN24C8 macrocycles preferentially, at high pH, deprotonation occurs with loss of hydrogen bonding and the macrocycles will move to the BIPY(2+) sites, where they can acquire some stabilizing [pi-pi] stacking interactions. Such mechanically interlocked molecules have been assembled from a trifurcated rig-like component wherein the dumbbell-like components of three [2]rotaxanes have one of their ends fused onto alternate positions (1,3,5) around a benzenoid core. The rig is mechanically interlocked by a platform based on a tritopic receptor, wherein either three benzo[24]crown-8 or three 2,3-naphtho[24]crown-8 macrocycles are fused onto a hexaoxatriphenylene core. The synthesis of these molecular elevators involves 1:1 complexation, followed by stoppering, i.e., feet are added to the rig. (1)H NMR spectroscopy and cyclic voltammetry, aided and abetted by absorption spectroscopy, have been employed to unravel the details of the mechanism by which the rig and platform components move on the alternate addition of base and acid. For each molecular elevator, the platform operates by taking three distinct steps associated with each of the three deprotonation/reprotonation processes. Thus, molecular elevators are more reminiscent of a legged animal than they are of passengers on freight elevators. 相似文献
5.
A [2]catenane, composed of a pi-electron-rich bis-1,5-dioxynaphthalene[38]crown10 (BDNP38C10) ring, mechanically interlocked with a large macrocycle containing two disubstituted tetraarylmethane "speed bumps" and two different pi-electron-deficient units--namely, naphthalene dimide (NpI) and bipyridinium (BIPY(2+)) units--has been synthesized from a [2]rotaxane, containing the former recognition unit, after performing two sequential Cu(I)-catalyzed azide-alkyne cycloadditions with a linker containing the latter recognition unit. The product, which exists as a single co-conformer, wherein the BDNP38C10 ring encircles the NpI unit, undergoes equilibration to give approximately equal amounts of the other co-conformer in which the BDNP38C10 ring encircles the BIPY(2+) unit. 相似文献
6.
Mixing the dipyrido[24]crown-8 derivatives carrying one or two formyl group(s) on the 4 position(s) of their pyridine ring(s) with a 3-fold symmetrical trisammonium ion template in a 3:1 ratio in CD3NO2 results in the formation of thermodynamically stable [4]pseudorotaxanes which, upon addition of a 1,3,5-trisaminobenzene cap, form mechanically interlocked molecular bundles with one and two caps, respectively, by virtue of dynamic imine bond formation. 相似文献
7.
This tutorial review describes the evolution of the field of chemical templation, in particular, emphasising the impact its application has made to the synthesis of mechanically interlocked structures. Recent advances in the use of negatively charged template species for the synthesis of interlocked structures are detailed, with the main focus of this review describing the development of a general anion templation strategy that combines anion recognition with ion-pairing. The versatility of this methodology is demonstrated by the chloride anion templated synthesis of a series of interpenetrated pseudorotaxane, rotaxane and catenane structures. Upon template removal, the mechanically interlocked rotaxanes and catenanes are shown to bind anions within their topologically unique anion binding clefts by virtue of electrostatic and hydrogen bonding interactions, exhibiting a strong selectivity for the chloride halide anion template. The incorporation of the photo-active rhenium(I) bipyridyl signalling group into the rotaxane structural framework highlights the potential of these interlocked systems in future chemical sensor design. 相似文献
8.
Hmadeh M Fahrenbach AC Basu S Trabolsi A Benítez D Li H Albrecht-Gary AM Elhabiri M Stoddart JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(22):6076-6087
The ability to control the kinetic barriers governing the relative motions of the components in mechanically interlocked molecules is important for future applications of these compounds in molecular electronic devices. In this Full Paper, we demonstrate that bipyridinium (BIPY2+) dications fulfill the role as effective electrostatic barriers for controlling the shuttling and threading behavior for rotaxanes and pseudorotaxanes in aqueous environments. A degenerate [2]rotaxane, composed of two 1,5‐dioxynaphthalene (DNP) units flanking a central BIPY2+ unit in the dumbbell component and encircled by the cyclobis(paraquat‐p‐phenylene) (CBPQT4+) tetracationic cyclophane, has been synthesized employing a threading‐followed‐by‐stoppering approach. Variable‐temperature 1H NMR spectroscopy reveals that the barrier to shuttling of the CBPQT4+ ring over the central BIPY2+ unit is in excess of 17 kcal mol?1 at 343 K. Further information about the nature of the BIPY2+ unit as an electrostatic barrier was gleaned from related supramolecular systems, utilizing two threads composed of either two DNP units flanking a central BIPY2+ moiety or a central DNP unit flanked by a BIPY2+ moiety. The threading and dethreading processes of the CBPQT4+ ring with these compounds, which were investigated by spectrophotometric techniques, reveal that the BIPY2+ unit is responsible for affecting both the thermodynamics and kinetics of pseudorotaxane formation by means of an intramolecular self‐folding (through donor–acceptor interactions with the DNP unit), in addition to Coulombic repulsion. In particular, the free energy barrier to threading (Δ${G{{{\ne}\hfill \atop {\rm f}\hfill}}}The ability to control the kinetic barriers governing the relative motions of the components in mechanically interlocked molecules is important for future applications of these compounds in molecular electronic devices. In this Full Paper, we demonstrate that bipyridinium (BIPY(2+)) dications fulfill the role as effective electrostatic barriers for controlling the shuttling and threading behavior for rotaxanes and pseudorotaxanes in aqueous environments. A degenerate [2]rotaxane, composed of two 1,5-dioxynaphthalene (DNP) units flanking a central BIPY(2+) unit in the dumbbell component and encircled by the cyclobis(paraquat-p-phenylene) (CBPQT(4+)) tetracationic cyclophane, has been synthesized employing a threading-followed-by-stoppering approach. Variable-temperature (1)H?NMR spectroscopy reveals that the barrier to shuttling of the CBPQT(4+) ring over the central BIPY(2+) unit is in excess of 17 kcal mol(-1) at 343 K. Further information about the nature of the BIPY(2+) unit as an electrostatic barrier was gleaned from related supramolecular systems, utilizing two threads composed of either two DNP units flanking a central BIPY(2+) moiety or a central DNP unit flanked by a BIPY(2+) moiety. The threading and dethreading processes of the CBPQT(4+) ring with these compounds, which were investigated by spectrophotometric techniques, reveal that the BIPY(2+) unit is responsible for affecting both the thermodynamics and kinetics of pseudorotaxane formation by means of an intramolecular self-folding (through donor-acceptor interactions with the DNP unit), in addition to Coulombic repulsion. In particular, the free energy barrier to threading (ΔG(f)(++)) of the CBPQT(4+) for the case of the thread composed of a DNP flanked by two BIPY(2+) units was found to be as high as 21.7 kcal mol(-1) at room temperature. These results demonstrate that we can effectively employ the BIPY(2+) unit to serve as electrostatic barriers in water in order to gain control over the motions of the CBPQT(4+) ring in both mechanically interlocked and supramolecular systems. 相似文献
9.
Scarff CA Snelling JR Knust MM Wilkins CL Scrivens JH 《Journal of the American Chemical Society》2012,134(22):9193-9198
Mechanically interlocked polymers can possess significant additional physical properties, in comparison to those associated with their constituent parts. Their unique properties make them attractive for a range of potential applications, such as as biomaterials and molecular machines. Their efficient and reproducible synthesis is therefore of much interest. Both their synthesis and subsequent characterization are intriguing yet demanding. The properties of mechanically interlocked polymeric systems depend not only on the properties of their individual components but also on the topology of the subsequent product. Here traveling wave ion mobility mass spectrometry has been used to investigate the structural properties of a polyrotaxane system. Ion mobility studies reveal that this system remains linear in form with increase in size. Both ion mobility studies and tandem mass spectrometry studies indicate that the macrocycle preferentially remains associated with the ammonium moiety of the polymeric repeat unit and is impeded from moving freely along the axle. This is consistent with NMR observations of the average structure. Analysis of mechanically interlocked polymers by ion mobility mass spectrometry provides additional structural insights into these systems relating to dynamics, heterogeneity, and topology. This molecule-specific information is vital in order to understand the origin of a system's functional properties. 相似文献
10.
Zhen Luo Dr. Xinhai Zhang Jun Zhao Ruixue Bai Dr. Chunyu Wang Yuanhao Wang Dr. Dong Zhao Prof. Xuzhou Yan 《Angewandte Chemie (International ed. in English)》2023,62(37):e202306489
Mechanical bonds have been utilized as promising motifs to construct mechanically interlocked aerogels (MIAs) with mechanical adaptivity and multifunctionality. However, fabricating such aerogels with not only precise chemical structures but also dynamic features remains challenging. Herein, we present MIAs carrying dense [2]rotaxane units, which bestow both the stability and flexibility of the aerogel network. Owing to the stable chemical structure of a [2]rotaxane, MIAs possessing a precise and full-scale mechanically interlocked network could be fabricated with the aid of diverse solvents. In addition, the dynamic nature of the [2]rotaxane resulted in morphologies and mechanical performances of the MIAs that can be dramatically modulated under chemical stimuli. We hope that the structure–property relationship in MIAs will facilitate the development of mechanically interlocked materials and provide novel opportunities toward constructing smart materials with multifunctionalities. 相似文献
11.
The quest to construct mechanically interlocked polymers, which present precise monodisperse primary structures that are produced both consistently and with high efficiencies, has been a daunting goal for synthetic chemists for many years. Our ability to realise this goal has been limited, until recently, by the need to develop synthetic strategies that can direct the formation of the desired covalent bonds in a precise and concise fashion while avoiding the formation of unwanted kinetic by-products. The challenge, however, is a timely and welcome one, as a consequence of, primarily, the potential for mechanically interlocked polymers to act as dynamic (noncovalent) yet robust (covalent) new materials for a wide array of applications. One such strategy which has been employed widely in recent years to address this issue, known as Dynamic Covalent Chemistry (DCC), is a strategy in which reactions operate under equilibrium and so offer elements of "proof-reading" and "error-checking" to the bond forming and breaking processes such that the final product distribution always reflects the thermodynamically most favourable compound. By coupling DCC with template-directed protocols, which utilise multiple weak noncovalent interactions to pre-organise and self-assemble simpler small molecular precursors into their desired geometries prior to covalent bond formation, we are able to produce compounds with highly symmetric, robust and complex topologies that are otherwise simply unobtainable by more traditional methods. Harnessing these strategies in an iterative, step-wise fashion brings us ever so much closer towards perfecting the controlled synthesis of high order main-chain mechanically interlocked polymers. This tutorial review focuses (i) on the development of DCC-namely, the formation of dynamic imine bonds-used in conjunction with template-directed protocols to afford a variety of mechanically interlocked molecules (MIMs) and ultimately (ii) on the synthesis of highly ordered poly[n]rotaxanes with high conversion efficiencies. 相似文献
12.
Integrative Self‐Sorting: One‐Pot Synthesis of a Hetero[4]rotaxane from a Daisy‐Chain‐Containing Hetero[4]pseudorotaxane
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The structural complexity of mechanically interlocked molecules are very attractive to chemists owing to the challenges they present. In this article, novel mechanically interlocked molecules with a daisy‐chain‐containing hetero[4]rotaxane motif were efficiently synthesized. In addition, a novel integrative self‐sorting strategy is demonstrated, involving an ABB‐type (A for host, dibenzo‐24‐crown‐8 (DB24C8), and B for guest, ammonium salt sites) monomer and a macrocycle host, benzo‐21‐crown‐7 (B21C7), in which the assembled species in hydrogen‐bonding‐supported solvent only includes a novel daisy‐chain‐containing hetero[4]pseudorotaxane. The found self‐sorting process involves the integrative recognition between B21C7 macrocycles and carefully designed components simultaneously containing two types of secondary ammonium ions and a host molecule, DB24C8 crown ether. The self‐sorting strategy is integrative to undertake self‐recognition behavior to form one single species of pseudorotaxane compared with the previous report. This self‐sorting system can be used for the efficient one‐pot synthesis of a daisy‐chain‐containing hetero[4]rotaxane in a good yield. The structure of hetero[4]rotaxane was confirmed by 1H NMR spectroscopy and high‐resolution electrospray ionization (HR‐ESI) mass spectrometry. 相似文献
13.
Spruell JM Dichtel WR Heath JR Stoddart JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(14):4168-4177
A one-pot sequential Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) strategy is presented for the synthesis of constitutionally unsymmetrical cyclobis(paraquat-p-phenylene)-based rotaxanes in good yields from simple starting materials. The methodology consists of performing multiple CuAAC reactions to stopper a pseudorotaxane in a stepwise manner, the order of which is controlled through silyl-protection and Ag(I)-catalyzed deprotection of a terminal alkyne. The methodology is highlighted by the synthesis of an amphiphilic branched [4]rotaxane. The methodology increases the ability to access ever more complicated mechanically interlocked compounds to serve in devices as sophisticated and functional molecular machinery. 相似文献
14.
Shijun Li Bo Zheng Jianzhuang Chen Shengyi Dong Zhi Ma Feihe Huang Harry W. Gibson 《Journal of polymer science. Part A, Polymer chemistry》2010,48(18):4067-4073
Based on the dibenzo‐24‐crown‐8/1,2‐bis(pyridinium)ethane recognition motif, a hyperbranched mechanically interlocked polymer was prepared by polyesterification of an easily available dynamic trifunctional AB2 pseudorotaxane monomer. It was characterized by various techniques including 1H NMR, COSY, NOESY, GPC, viscosity, TGA, dynamic laser light scattering, AFM, and SEM. Its GPC Mn was determined to be 191 kDa with polydispersity 1.7 and its hydrodynamic diameter in a dilute solution in acetone was about 70 nm. This measured Mn value corresponds to about 93 repeating units. The study reported here presents not only a new polymer topology but also a novel and convenient way to prepare mechanically interlocked polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4067–4073, 2010 相似文献
15.
Dr. Jingjing Yu Dr. Marius Gaedke Dr. Fredrik Schaufelberger 《European journal of organic chemistry》2023,26(8):e202300101
Mechanically interlocked molecules have found extensive applications in areas all across the physical sciences, from materials to catalysis and sensing. However, introducing mechanical bonds and entanglements at the molecular level is still a significant challenge due to the inherent restriction in entropy needed to preorganize strands before interlocking. Over the last decade, dynamic covalent chemistry has emerged as one of the most efficient methods of forming rotaxanes, catenanes and molecular knots. By using reversible bonds such as imines, disulfides and boronate esters, one can use the inherent error-correction in these linkages to form interlocked architectures with high fidelity and often in excellent yields. This review reports on recent advances in the use of dynamic covalent chemistry to make mechanically interlocked molecules, systematically surveying clipping, capping and templating approaches with dynamic bonds. Furthermore, it is also discussed how dynamic bonds can be used to control motion, co-conformational expression and catalytic activity in mechanically interlocked molecular machinery. 相似文献
16.
David A. Tramontozzi Dr. Natalie D. Suhan Dr. S. Holger Eichhorn Prof. Stephen J. Loeb Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4466-4476
Fréchet‐type dendrons (G0–G3) were added as both axle stoppering units and cyclic wheel appendages in a series of [2]rotaxanes, [3]rotaxanes, and molecular shuttles that employ 1,2‐bis(pyridinium)ethane axles and 24‐membered crown ethers wheels. The addition of dendrimer wedges as stoppering units dramatically increased the solubility of simple [2]rotaxanes in nonpolar solvents. The X‐ray structure of a G1‐stoppered [2]rotaxane shows how the dendritic units affect the structure of the interlocked components. Increased solubility allows observation of how the interaction of dendritic units on separate components in interlocked molecules influences switching properties and molecular size. In a series of [2]rotaxane molecular shuttles incorporating two recognition sites, it was demonstrated that an increase in generation on either the stoppering unit or cyclic wheel could influence both the rate of shuttling and the site preference of the wheel on the axle. 相似文献
17.
Although there are many examples of catenanes, those of more complex mechanically interlocked molecular architectures are rare. Additionally, little attention has been paid to the degradation of such interlocked systems into their starting complexes, although formation and degradation are complementary phenomena and are equally important. Interlocked metallohelicate, [(Pd(2)L(4))(2)](8+) (2(8+)), is a quadruply interlocked molecular architecture consisting of two mechanically interlocked monomers, [Pd(2)L(4)](4+) (1(4+)). 2(8+) has three internal cavities, each of which encapsulates one NO(3)(-) ion (1:3 host-guest complex, 2?(NO(3)|NO(3)|NO(3))(5+)) and is characterized by unusual thermodynamic stability. However, both the driving force for the dimerization and the origin of the thermodynamic stability remain unclear. To clarify these issues, BF(4)(-), PF(6)(-), and OTf(-) have been used to demonstrate that the dimerization is driven by the anion template effect. Interestingly, the stability of 2(8+) strongly depends on the encapsulated anions (2?(NO(3)|NO(3)|NO(3))(5+) ? 2?(BF(4)|BF(4)|BF(4))(5+)). The origins of this differing thermodynamic stability have been shown through detailed investigations to be due to the differences in the stabilization of the interlocked structure by the host-guest interaction and the size of the anion. We have found that 2-naphthalenesulfonate (ONs(-)) induces the monomerization of 2?(NO(3)|NO(3)|NO(3))(5+) via intermediate 2?(ONs|NO(3)|ONs)(5+), which is formed by anion exchange. On the basis of this finding, and using p-toluenesulfonate (OTs(-)), the physical separation of 2?(NO(3)|NO(3)|NO(3))(5+) and 1(4+) as OTs(-) salt was accomplished. 相似文献
18.
Haxton KJ Cole-Hamilton DJ Morris RE 《Dalton transactions (Cambridge, England : 2003)》2007,(31):3415-3420
A method of calculating the bite (P-M-P) angle for dendritic ligands is reported. Diphenylphosphine terminated dendritic ligands were modified with either a single rhodium or a rhodium complex [HRh(CO)(2)] and molecular dynamics techniques used to run simulations to determine the dynamic bite angle (beta(d)) as a time averaged property. The effects of changing the composition of the dendritic branches is investigated and comparison with experimental hydroformylation data reveals that the dendrimer with the highest linear: branched ratio also has a dynamic bite angle closest to the theoretical ideal value of 120 degrees . 相似文献
19.
Zhou W Li J He X Li C Lv J Li Y Wang S Liu H Zhu D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(2):754-763
A [2]rotaxane-based molecular shuttle comprised a macrocycle mechanically interlocked to a chemical "dumbbell" has been prepared in high yields by a thermodynamically controlled, template-induced clipping procedure. This molecular shuttle has two different recognition sites, namely, -NH2 +- and amide, separated by a phenyl unit. The macrocycle exhibits high selectivity for the -NH2+- recognition sites in the protonated form through noncovalent interactions, which include 1) N+-H...O hydrogen bonds; 2) C-H...O interactions between the CH2NH2+CH2 protons on the thread and the oligo(ethylene glycol) unit in the macrocycle; 3) pi...pi stacking interaction between macrocycle and aromatic unit. Upon deprotonation of the [2]rotaxane the macrocycle glides to the amide recognition site due to the hydrogen bonds between the -CONH- group and the oligo(ethylene glycol) unit in the macrocycle. The deprotonation process requires about 10 equivalents of base (iPr2NEt) in polar acetone, while the amount of base is only 1.2 equivalents in apolar tetrachloroethane. Upon addition of Li+, the conformation of the [2]rotaxane was altered as a result of the collective interactions of 1) hydrogen bonds between pyridine nitrogen and amide hydrogen atoms; 2) coordination between the oligo(ethylene glycol) unit, amide oxygen atom and Li+ cation. Then, when Zn2+ ions are added, the macrocycle returns to the deprotonated -NH- recognition site owing to coordination of the macrocycle and -NH- from the axle with the Zn2+ ion. All the above-mentioned movement processes are reversible through the alternate addition of TFA/iPr2NEt, Li/[12]-crown-4 and Zn2+/ethylenediaminetetraacetate (EDTA), by virtue of hydrogen bonding and metal-ion complexation. Significantly, the three independent movement processes are all accompanied by fluorescent responses: 1) complete repression in the protonated form; 2) low-level expression in the deprotonated form; 3) medium-level expression following addition of Li+; 4) high-level expression on complexation with Zn2+. 相似文献
20.
Prof. Eugenio Coronado Prof. Pablo Gaviña Julia Ponce Dr. Sergio Tatay 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(23):6939-6950
The present work reports the introduction of pyridine bisamine terdentate ligands in the structure of a pirouetting copper rotaxane. Rotaxane 2 [PF6] constitutes the first example of the incorporation of imine‐based dynamic covalent chemistry in the synthesis of switchable copper‐complexed interlocked systems. In this rotaxane, the substitution of the classical terpyridine terdentate unit by a pyridine bisamine moiety has led to a significant stabilization of the pentacoordinated site. That fact has been evidenced by EPR spectroscopy and cyclic voltammetry. Regarding the tetracoordinated site, the congestion around the coordination sphere has been reduced to accelerate the typically slow reorganization of the CuII. Ethynyl‐3,8‐substitution on the axis phenanthroline along with the 2,9‐diphenyl‐1,10‐phenanthroline (dpp) present in the macrocycle afforded a very stable coordination environment for CuI, which is at the same time labile upon oxidation. In summary, the incorporation of a pyridine bisamine unit as a terdentate ligand and the optimization of the bidentate ligand of the axle not only has led to a simplification of the synthetic procedures, but it has also given rise to a bistable systems with an enhanced energetic separation between states and an acceleration of the reorganization processes. Thus far, rotaxane 2 [PF6] presents the fastest switching cycle reported to date in copper‐interlocked dynamic systems. 相似文献